Ferroresonant transformer for use in uninterruptible power supplies

ABSTRACT

A ferroresonant transformer is adapted to be connected to a primary power source, an inverter system, and a resonant capacitor. The ferroresonant transformer comprises a core, a main shunt arranged to define a primary side and a secondary side of the ferroresonant transformer, first windings arranged on the primary side of the ferroresonant transformer, second windings arranged on the secondary side of the ferroresonant transformer, and third windings arranged on the secondary side of the ferroresonant transformer. The first windings are operatively connected to the primary power source.

RELATED APPLICATIONS

This application U.S. patent application Ser. No. 14/071,497, filed Nov.4, 2013, is a continuation of U.S. patent application Ser. No.12/803,787 filed Jul. 7, 2010, now U.S. Pat. No. 8,575,779 which issuedNov. 5, 2013.

U.S. patent application Ser. No. 12/803,787 claims benefit of U.S.Provisional Patent Application Ser. No. 61/305,926 filed Feb. 18, 2010.

The contents of all related applications listed above are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates the generation of a standby power signaland, more specifically, to uninterruptible power supply systems andmethods using ferroresonant transformers.

BACKGROUND

Uninterruptible power supplies (UPS's) have long been used to provide atleast temporary auxiliary power to electronic devices. Typically, a UPSis configured to switch between a primary power source and a standbypower source as necessary to maintain constant power to a load.

For example, the primary power source may be a utility power supply, andthe standby power source may take the form of a battery system. The UPSwill normally operate in a line mode in which the utility power signalis passed to the load when the utility power signal is within predefinedparameters. In the line mode, the UPS will typically also charge thebattery system. When the utility power falls outside of the predefinedparameters, the UPS will switch to standby mode in which an AC signal isgenerated based on the energy stored in the battery system.

A class of UPS's employs a ferroresonant transformer. A ferroresonanttransformer is a saturating transformer that employs a tank circuitcomprised of a resonant winding and capacitor to produce a nearlyconstant average output even if the input to the transformer varies. Atypical UPS employing a ferroresonant transformer takes advantage of thevoltage regulating properties of a ferroresonant transformer in bothline and standby modes. In the context of a UPS, a ferroresonanttransformer thus provides surge suppression, isolation, short circuitprotection, and voltage regulation without the use of active components.

Conventionally, a ferroresonant transformer configured for use in a UPSsystem includes a core and an inductor arranged relative to the core todefine: (a) a primary or input side of the transformer and (b) asecondary or output side of the transformer. A conventionalferroresonant transformer used in a UPS will further comprise inputwindings and inverter (resonant) windings arranged on the primary orinput side and output windings on the secondary or output side.

An object of the present invention is to provide improved ferroresonanttransformers for use in UPS systems.

SUMMARY

The present invention may be embodied as a ferroresonant transformeradapted to be connected to a primary power source, an inverter system,and a resonant capacitor. The ferroresonant transformer comprises acore, a main shunt arranged to define a primary side and a secondaryside of the ferroresonant transformer, first windings arranged on theprimary side of the ferroresonant transformer, second windings arrangedon the secondary side of the ferroresonant transformer, and thirdwindings arranged on the secondary side of the ferroresonanttransformer. The first windings are operatively connected to the primarypower source.

The present invention may also be embodied as an uninterruptible powersupply system adapted to be connected to a primary power source, abattery system, and a load. An uninterruptible power supply of thepresent invention comprises a ferroresonant transformer, an inverter,and a resonant capacitor. The ferroresonant transformer comprises acore, a main shunt, and first, second, and third windings. The mainshunt is arranged relative to the core to define a primary side and asecondary side of the ferroresonant transformer. The first windings arearranged on the primary side of the ferroresonant transformer. Thesecond windings are arranged on the secondary side of the ferroresonanttransformer. The third windings arranged on the secondary side of theferroresonant transformer. The inverter is operatively connected to thesecond windings. The resonant capacitor is operatively connected to thethird windings. The first windings are operatively connected to theprimary power source. The inverter is operatively connected to thebattery system. The resonant capacitor is operatively connected to theload.

The present invention may also be embodied as a method of supplyingpower to a load based on an AC power signal and a DC power signal, themethod comprising the following steps. A ferroresonant transformer isformed by arranging a main shunt relative to a core to define a primaryside and a secondary side of the ferroresonant transformer, arrangingfirst windings on the primary side of the ferroresonant transformer,arranging second windings on the secondary side of the ferroresonanttransformer, and arranging third windings on the secondary side of theferroresonant transformer. An inverter is operatively connected to thesecond windings. A resonant capacitor is operatively connected to thethird windings. The load is operatively connected to the resonantcapacitor. Power is supplied to the load based on the AC power signal ina line mode. The inverter is operated based on the DC power signal toprovide power to the load in a standby mode.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a first embodiment of anuninterruptible power supply system using a ferroresonant transformersystem constructed in accordance with, and embodying, the principles ofthe present invention;

FIG. 2 is a somewhat schematic view of a ferroresonant transformerforming a part of the UPS system depicted in FIG. 1;

FIG. 3 is a perspective view of the ferroresonant transformer depictedin FIG. 2;

FIG. 4 is a side elevation view of the ferroresonant transformerdepicted in FIGS. 2 and 3; and

FIG. 5 is a section view taken along lines 5-5 in FIG. 4.

DETAILED DESCRIPTION

Referring initially to FIG. 1 of the drawing, depicted therein is afirst example of an uninterruptible power supply (UPS) system 20constructed in accordance with, and embodying, the principles of thepresent invention.

The example UPS system 20 supplies power to a load 22 based on a primarypower signal present on an AC power line 24 (line mode) or a secondarypower signal generated by a battery pack 26 (standby mode). While theexample secondary power signal is generated by a battery pack in theexample UPS system 20, alternative power sources such as generators,fuel cells, solar cells, and the like may be used as the secondary powersource.

The example UPS system 20 comprises an input section 30, an outputsection 32, an inverter section 34, a cable assembly 36, and aferroresonant transformer 38.

The example input section 30 comprises a main switch 40 and first andsecond select switches 42 and 44. The example output section 32comprises an output or resonant capacitor 50 and, optionally, a selectswitch 52 and a filter capacitor 54.

When the select switch 52 is closed, the output capacitor 50 forms aresonant or tank circuit with the transformer 38 as will be described infurther detail below. When the select switch 52 is open, the outputcapacitor 50 is removed from the circuit formed by the output section 32and transformer 38, and the filter capacitor 54 filters the output ofthis circuit.

The inverter section 34 comprises an inverter circuit 60. The invertercircuit 60 may be an H-bridge circuit or any other circuit capable ofproducing an appropriate AC power signal based on a DC power signalobtained from the battery pack 26. In particular, the inverter circuit60 is pulse-width modulated, and the inverter section 34 functions as aswitch mode power supply when the UPS system operates in the standbymode. The inverter section 34 and the inverter circuit 60 are or may beconventional and will not be described herein in further detail.

A controller 62 may be optionally included in the inverter section 34.If used, the controller 62 operates the switches 40 and 52 and controlsthe inverter circuit 60. The controller 62 may further control thecharging of the battery pack 26 when the UPS system 20 operates in linemode based on the temperature, voltage, and/or current signalsassociated with the battery pack 26.

The ferroresonant transformer 38 comprises a core 70, input windings 72,an inductor 74, inverter windings 76, and output windings 78. The core70 is or may be a conventional laminate structure. As shown in FIG. 2,the inductor 74 defines a primary side 80 and a secondary side 82 of thetransformer 38. In the example transformer 38, only the input windings72 are on the primary side 80 of the transformer 38. The inverterwindings 76 and output windings 78 are on the secondary side 82 of thetransformer 38. In particular, the output windings 78 are arrangedbetween the inverter windings 76 and the inductor 74, and the inductor74 is arranged between the output windings 78 and the input windings 72.

As perhaps best shown in FIGS. 3 and 5, the transformer 38 depicted inFIGS. 1 and 2 defines the following arrangement of windings and shunts:the input windings 72, a large (or main) shunt formed by the inductor74, output windings 78, and inverter windings 76. FIGS. 3 and 5 furtherillustrate that, in the example transformer 38, a small (or minor) shunt90 is arranged between the output windings 78 and the inverter windings76. The small shunt 90 does not significantly affect the electromagneticproperties of the transformer 38 in the context of the overall UPSsystem 20 but is used in the example transformer 38 to allow thetransformer 38 to operate as described herein in the context of the UPSsystem 20.

In the line mode, the AC power line 24 forms a primary power source thatcauses a primary signal to be present on the input windings 72. Theinput windings 72 are electromagnetically coupled to the output windings78 such that a first output signal is supplied to one or both of theloads 22 a and 22 b when the UPS system 20 operates in the line mode.

In the standby mode, the battery pack 26 and inverter section 34 form asecondary power source that causes a secondary signal to be present onthe inverter windings 76. The inverter windings 76 areelectromagnetically coupled to the output windings 78 such that a secondoutput signal is supplied to one or both of the loads 22 a and 22 b whenthe UPS system 20 operates in the standby mode.

The construction details of the transformer 38 are not critical to thegeneral principles of the present invention and will depend upon aparticular implementation of the UPS system 20 in which the transformer38 is designed to operate. The example transformer 38 has the followingcharacteristics:

stacking 3 × 3 interleaved stack height approximately 109.73 MM (4.32″)shunts positioned in cores such that there is equal overhang on bothsides keeper cut from E lamination at both ends of stack; tape tightlyacross keeper after E-I compaction to reduce noise lamination compactE-I lamination together without air gap sleevings nylon sleevings usedwith bolts shims use wood shims to fill in gaps between windings andcore small shunt approximately 2.00 mm (0.075″) thick (4 pcs grade H50or 3 pcs M54 shunt lamination); polyester tape large shunt approximately16 mm (0.625″) thick (stack height adjusted to meet short circuitcurrent requirement); polyester tape core E-I lamination; grainorientation as shown in FIG. 3 varnish penetrate at least 80% of thewindings and be fully cured

The example cable assembly 36 connects the output section 32 to one offirst and second example loads 22 a or 22 b. In particular, the cableassembly 36 comprises first and second winding connectors 120 and 122operatively connected to a first end 124 of the output windings 78. Asecond end 126 of the output windings 78 is connected to the outputcapacitor 50. The cable assembly 36 further comprises first and secondtap connectors 130 and 132 operatively connected to first and secondintermediate points 134 and 136, respectively, of the output windings78. The example cable assembly 36 additionally comprises a selectioncable 140 comprising a selection connector 142 and first and secondoutput connectors 144 and 146. The first load 22 a comprises first andsecond load connectors 150 and 152, while the second load 22 b comprisessecond and third load connectors 154 and 156.

Using the example cable assembly 36, the selection connector 142 isconnected to either the first tap connector 130 or the second tapconnector 132 depending upon the voltage requirements of the loads 22 aand 22 b. The first and third load connectors 150 and 154 are connectedto the first and second winding connectors 120 and 122, and the secondand fourth winding connectors 152 and 156 are connected to the first andsecond output connectors 144 and 146, respectively. The cable assembly36 thus allows one or both of the loads 22 a and 22 b to be connected tothe output section 32 and the output windings 78 and, more specifically,to an appropriate portion of the output windings 78 as determined by thefirst and second tap connectors 130 and 132. The selection of theappropriate tap connector 130 or 132 is based on the voltagerequirements of the loads 22 a and 22 b.

Given the foregoing, it should be apparent that the principles of thepresent invention may be embodied in forms other than those describedabove. The scope of the present invention should thus be determined theclaims to be appended hereto and not the foregoing detailed descriptionof the invention.

What is claimed is:
 1. A ferroresonant transformer adapted to beconnected to a primary power source, an inverter system, and a resonantcapacitor, the ferroresonant transformer comprising: a core; a mainshunt arranged to define a primary side and a secondary side of theferroresonant transformer; first windings arranged on the primary sideof the ferroresonant transformer; second windings arranged on thesecondary side of the ferroresonant transformer; and third windingsarranged on the secondary side of the ferroresonant transformer; whereinthe first windings are configured to be operatively connected to theprimary power source; the second windings are configured to beoperatively connected to the inverter system; and the third windings areconfigured to be directly connected to the resonant capacitor.
 2. Aferroresonant transformer as recited in claim 1, in which the main shuntis formed by an inductor.
 3. A ferroresonant transformer as recited inclaim 1, further comprising a minor shunt arranged between the secondwindings and the third windings.
 4. An uninterruptible power supplysystem adapted to be connected to a primary power source, a batterysystem, and a load, the uninterruptible power supply comprising: aferroresonant transformer comprising a core; a main shunt arrangedrelative to the core to define a primary side and a secondary side ofthe ferroresonant transformer; first windings arranged on the primaryside of the ferroresonant transformer; second windings arranged on thesecondary side of the ferroresonant transformer; and third windingsarranged on the secondary side of the ferroresonant transformer; and aninverter, where the inverter is operatively connected to the secondwindings; a resonant capacitor, where the resonant capacitor isoperatively connected to the third windings; and a select switch:wherein the first windings are operatively connected to the primarypower source; the inverter is operatively connected to the batterysystem; the resonant capacitor is operatively connected to the load; ina line mode, power flows from the primary source to the load through theferroresonant transformer; and in a standby mode, power flows from theinverter to the load through the ferroresonant transformer, where theselect switch is configured to disconnect the reasonant capacitor fromthe third windings when the uninterruptible power supply is in thestandby mode.
 5. An uninterruptible power supply as recited in claim 4,in which the main shunt is formed by an inductor.
 6. An uninterruptiblepower supply as recited in claim 4, in which the ferroresonanttransformer further comprises a minor shunt arranged between the secondwindings and the third windings.
 7. An uninterruptible power supply asrecited in claim 4, in which the inverter is pulse-width modulated. 8.An uninterruptible power supply as recited in claim 4, in which theinverter is a switch mode power supply.
 9. An uninterruptible powersupply as recited in claim 4, in which the primary power source is autility power supply.
 10. An uninterruptible power supply as recited inclaim 4, further comprising a filter capacitor operatively connectedacross at least a portion of the third windings.
 11. A method ofsupplying power to a load based on an AC power signal and a DC powersignal, the method comprising the steps of: forming a ferroresonanttransformer by arranging a main shunt relative to a core to define aprimary side and a secondary side of the ferroresonant transformer;arranging first windings on the primary side of the ferroresonanttransformer; arranging second windings on the secondary side of theferroresonant transformer; arranging third windings on the secondaryside of the ferroresonant transformer; operatively connecting theinverter to the second windings; and operatively connecting a resonantcapacitor to the third windings; operatively connecting the load to theresonant capacitor; supplying power to the load through theferroresonant transformer based on the AC power signal in a line mode;operating the inverter based on the DC power signal to provide power tothe load through the ferroresonant transformer in a standby mode; anddisconncecting the reasonant capacitor from the third windings when theuninterruptible power supply is in the standby mode.
 12. A method asrecited in claim 11, further comprising the step of operating theinverter to generate a battery charge signal in the line mode.
 13. Amethod as recited in claim 11, in which the step of arranging a mainshunt relative to a core comprises the step of providing an inductor.14. A method as recited in claim 11, in which the step of forming theferroresonant transformer further comprises the step of arranging aminor shunt between the second windings and the third windings.
 15. Amethod as recited in claim 11, in which the step of operating theinverter in standby mode further comprises the step of pulse-widthmodulating the DC power signal.
 16. A method as recited in claim 11, inwhich the step of operating the inverter in standby mode furthercomprises the step of operating the inverter as a switch mode powersupply.
 17. A method as recited in claim 11, further comprising the stepof operatively connecting a filter capacitor across at least a portionof the third windings.
 18. A method of supplying power to a load basedon an AC power signal and a DC power signal, the method comprising thesteps of: forming a ferroresonant transformer by arranging a main shuntrelative to a core to define a primary side and a secondary side of theferroresonant transformer; arranging first windings on the primary sideof the ferroresonant transformer; arranging second windings on thesecondary side of the ferroresonant transformer; arranging thirdwindings on the secondary side of the ferroresonant transformer;operatively connecting the inverter to the second windings; operativelyconnecting a filter capacitor across at least a portion of the thirdwindings; operatively connecting a resonant capacitor to the thirdwindings; operatively connecting the load to the resonant capacitor;supplying power to the load based on the AC power signal in a line mode;operating the inverter based on the DC power signal to provide power tothe load in a standby mode; and disconnecting the reasonant capacitorfrom the third windings when the uninterruptible power supply is in thestandby mode.